1. Field of the Invention
The present invention relates to an image pickup apparatus that performs focus detection using an image sensor by a phase difference detection method.
2. Description of the Related Art
The focus detection by the phase difference detection method detects a phase difference between paired object images formed by light fluxes from mutually different areas of an exit pupil of an image capturing optical system to detect a focus state of the image capturing optical system. Japanese Patent Laid-Open No. 2001-83407 discloses an image pickup apparatus that performs such focus detection by the phase difference detection method by using an image sensor photoelectrically converting an object image to produce image data. The image sensor used for this disclosed image pickup apparatus has, for each pixel, one microlens and two photoelectric conversion portions. The image pickup apparatus reads signals from the two photoelectric conversion portions separately (independently) from each other to obtain paired image signals corresponding to the paired object images, thereby enabling detection of a phase difference of the paired object images. Moreover, adding the signals read from the two photoelectric conversion portions enables production of the image data.
However, the image pickup apparatus disclosed in Japanese Patent Laid-Open No. 2001-83407 requires to read the signals for detecting the phase difference separately (independently) from the two photoelectric conversion portions in each pixel, which doubles a signal reading time for one pixel as compared with a case of reading the signal from one photoelectric conversion portion in each pixel.